This invention relates generally to improvements in attaching a friction pad to a metal support plate and more particularly to improvements in a riveted brake assembly in which a brake friction pad is riveted to a metal disc plate or brake shoe used in automobiles and the like.
It has long been a practice to attach friction pads to metal support plates using rivets. Each rivet is clinched in counter sunk or counter bored holes in the friction pad which are aligned with holes in a metal support plate, typical constructions being shown in exemplary U.S. Pat. Nos. 1,875,374-Gallup; 2,096,598-Sheane; and 2,400,015-Mathieson. The types of rivets used in attachment of friction pads to support plates may either be solid, partially solid, or in hollow tubular form, sometimes termed an "eyelet." The rivet includes a cylindrical shank which is inserted through aligned pairs of holes in the friction pad and the support plate and has an enlarged head which rests upon the friction pad in the recessed hole. In the case of an eyelet, the head often most conveniently comprises a flanged end of the tubular member. Thereafter, the rivet is clinched between a driver on the head side and an anvil on the other end designed to curl and upset the tip of the rivet so that it firmly attaches the pad to the support plate and expands laterally into the aligned holes.
Variations in the diameters of the friction pad holes and support plate holes have led to the use of slightly undersized shanks on the rivets in order to accommodate these diametral variations, as well as providing for possible misalignment of the friction pad holes with respect to the support plate holes. This has led to lateral clearances between the outside of the clinched rivet and the friction pad which in turn have allowed the pad to shift laterally on the support plate in the case of extreme braking forces. This is accentuated by variations in thickness of the pad and plate members due to manufacturing tolerances. Particularly, the use of counterbored holes in disk brake pads, when combined with flat disk brake plates, is more prone to lateral shifting of the friction pad than was the case when using counter sunk holes in curved brake linings. Since the friction pads are made of relatively brittle or weak material, the shifting has led to excessive wear or crumbling of the friction pad around the rivet hole which requires premature replacement of the pad.
Various suggestions for overcoming the aforesaid problems have included the proposal of a tapered shank rivet as disclosed in U.S. Pat. 4,146,118-Zankl in which the volume of the rivet shank is calculated to be equal to the volumes of the rivet openings. A tapered rivet head rests in a pad hole which is smaller in diameter than the support plate hole. This construction requires a relatively short cavity in the tip of the solid rivet and depends upon lateral plastic flow of the dead-soft rivet to completely fill the support plate hole with metal.
Rivets for applications other than friction pads have been proposed in the past with a cylindrical shoulder or step between the head and the cylindrical shank. Such types of rivets are well-known for providing hinge pins, in order to provide clearance between the head and the shank as shown in U.S. Pat. No. 3,505,923, for example. However, these rivets require lateral clearance around the shoulder in order to function.
A proposal involving a shoulder on a rivet in a brake assembly is described in U.S. Pat. No. 3,767,018-Gordon for manufacture of a molded friction pad for a brake lining. A rivet with a shoulder is shown preclinched on a support plate in U.S. Pat. No. 3,767,018 to provide longitudinal clearance between the rivet head and the shoe prior to the molding step. This method is useful for construction of a brake lining from flowable uncured friction material which could otherwise flow through the rivet hole beneath the head of the rivet. The shoulder of the rivet must be larger than the hole in the support plate and must bear on the support plate in order to prevent leakage of the moldable friction material.
Accordingly, one object of the present invention is to provide an improved rivet brake assembly with an improved rivet for attachment of a friction pad to a metal support plate.
Another object of the invention is to provide an improved brake assembly which reduces wear and lateral shifting of the pad with respect to the support plate.
Still another object of the invention is to provide an improved eyelet rivet for attachment of a friction pad to a metal support plate.